Characteristic impedances in output cylindrical coaxial cavity resonator of klystron

Cylindrical coaxial cavity resonator with shift-tubes coupled with rectangular waveguide is designed. The gap characteristic impedance and external quality factor of higher order transverse magnetic mode TM
₃₁₀
in the cavity are simulated with high frequency electromagnetic simulator ISFEL-3D. The ununiformity of the characteristic impedance resulted from the coupling aperture is reduced through introduction of concave delves on peripheral wall of the cavity.